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What were the rules for sidecars before the 1990 FIM F2 class? The best I can find is from Wikipedia

1954–1959 Side-Cars not exceeding 500 cc engine capacity.
1968–1974 Non-Championship event for Sidecars not exceeding 750 cc.
1975–1989 Sidecars not exceeding 1000 cc engine capacity.
1990– FIM Formula 2 Sidecar race for two-stroke engines not exceeding 350 cc or four-stroke engines not exceeding 600 cc.

What were the wheel sizes? When did the rear exit appear?

Does anyone have rules from those periods?

I stumbled upon the CRMC site - are those the most accurate rules for the periods?

Its all a bit complicated,and others on here are more qualified than me to advise,however,as a rough guide,some of the vintage outfits in the 1950s were rear exit,and rear exit for the kneelers seemed to start becoming the norm around 1978/1979ish.

The rules tended to change after certain innovations came along and the changes in design were independent of any rule changes, which makes it difficult to date a machine according to the regs alone. For example when the rear exits started and when wheel size changes happened weren't due to any real amendment of the rules. The rear exit was more down to passengers having less time to get from one side to the other ( and being up front tending to take drive off the back wheel with the increasing power outputs ) and tyre size changes were a natural progression.
Dad was still racing an NSU that was compliant with the CRMC definition of a classic into the early 80's, still front exit, still on 13" wheels. Obviously not competitive, but still within the rules in the 80's and quite possibly still now?
If you're looking for the original FIM rules for certain periods, you might do to try the FIM themselves and see if they have anything in their archives ?

Thanks Steve. A few of us on this side of the pond are trying to come up with a decent set of rules for a P3. After swilling a bunch of beers with Peter Essaff, I've learned that the '80s was ripe with different types of bikes and configurations. As you point out, it is difficult to establish a decent set of rules that is historically accurate.

It was a complete mix, so putting a bunch of similar machines into classes is contrived to my mind compared to the reality. It's just sharing trophies in a way that didnt happen at the time. Dad didnt get a trophy for beong tenth.